A typical water heater for residential hot water production and storage is an electrical resistance water heater and storage tank, although gas water heaters are also used to heat water in a storage tank. Water heaters typically include a storage tank defining a chamber for retention of water. A water inlet pipe is provided with a first connection for interconnection with a cold water supply line that conveys fresh, relatively cold water into the storage tank. In the case of electrical resistance water heaters, there are electrical resistance elements, within the storage tank, that heat the water.
An alternative method for heating water is an active desuperheater water heater. In one example of an active desuperheater water heater, the active desuperheater water heater uses a small pump to circulate water from a water storage tank, through a heat exchanger, and back into the water storage tank. The active desuperheater water heater intercepts the superheated hot gas that is rejected from an air conditioner or heat pump compressor, sitting outside the home, and transfers the heat to the water circulating through the heat exchanger. The active desuperheater water heater works only when the air conditioner or heat pump is operating in a cooling mode.
Another alternative method for heating water is a heat pump water heater. A heat pump water heater contains a fan, compressor, and evaporator configured to sit on top of the water heater storage tank. The heat pump water heater circulates a refrigerant through an evaporator and compressor, and uses a fan and evaporator to pull heat from air surrounding the heat pump water heater in order to heat the refrigerant. The heated refrigerant runs through a condenser coil within the water storage tank, transferring heat to the water stored therein.